The recent isolation of 4-androstene-3-Beta, 17 Beta-diol as a transformation product from incubation T. pyriformis with testosterone in this laboratory indicates that this protozoan has a dehydrogenase capable of reducing the 3-ketone of a steroid to a 3Beta-hydroxyl. Our objective is to purify and characterize the nature of this enzyme. The identification of several other transformation products is also being pursued in the hope of establishing that T. pyriformis has an isomerase that can transform a delta 4-steroid to a delta 5-steroid.